1. n. [Geology]

A record of the onset and duration of the multitude of episodes of reversal of the Earth's magnetic polarity, or geomagnetic polarity reversals. The GPTS was developed by thorough study of rocks from around the world, during which it was observed that rocks from specific time periods contained magnetic minerals whose orientation was opposite to that of the current magnetic field. By comparing the patterns of magnetic reversals with those of rocks of known age, the approximate ages of rocks can be established. This is particularly useful for basalts of the oceanic crust, which record the Earth's magnetic field as they solidify from molten lava symmetrically about the midocean ridges. The time scale has been accurately extended back to the Upper Jurassic, the age of oldest existing oceanic crust.

Alternate Form: geomagnetic polarity time scale